Repurposed Spacecraft to Orbit Dark Side of the Moon

Repurposed Spacecraft to Orbit Dark Side of the Moon

LOS ANGELES, California, October 28, 2010 (ENS) – A pair of NASA spacecraft that were supposed to be dead a year ago are instead flying to the Moon for a unique mission in lunar orbit.

“Their real names are THEMIS P1 and P2, but I call them ‘dead spacecraft walking,'” says Vassilis Angelopoulos of the University of California, Los Angeles, principal investigator of NASA’s new lunar mission. “Not so long ago, we thought they were goners. Now they are beginning a whole new adventure.”

“In collaboration with NASA’s Jet Propulsion Laboratory and University of California, Berkeley, we are flinging the satellites into interplanetary space to the point where the Earth’s gravity and Moon’s gravity are approximately equal,” he said.

An artist’s concept of the two ARTEMIS spacecraft in lunar orbit. (Image courtesy NASA)

One of the THEMIS satellites has been in the lunar environment since August 25, and the second arrived October 22, marking the start of NASA’s ARTEMIS mission to gather new scientific data in the Sun-Earth-Moon environment.

For six months, the two satellites will fly in orbits behind the Moon but will not orbit the Moon itself. This type of orbit relies on a precise balancing of Sun, Earth and Moon gravity.

Then, in April 2011, the spacecraft are scheduled to make elliptical orbits around the Moon, each providing data every second day for several years.

ARTEMIS scientists will use simultaneous measurements of particles and electric and magnetic fields from the satellites to provide the first three-dimensional perspective of how energetic particle acceleration occurs near the Moon’s orbit, in the distant magnetosphere and in the solar wind.

Observing the space environment behind the dark side of the Moon – the greatest known vacuum in the solar system – the two satellites will provide new operational data that will help NASA plan future Moon missions.

“We will study the space environment around the Earth and around the Moon, which are not well understood,” Angelopoulos said. “ARTEMIS will provide unprecedented data and will go where no spacecraft have gone before.

Earth and Moon as seen from Mars. This image was taken October 3, 2007, by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter. (Photo courtesy NASA)

“ARTEMIS is going to give us a fundamental new understanding of the solar wind,” predicts David Sibeck, ARTEMIS project scientist at the Goddard Space Flight Center in Maryland. “And that’s just for starters.”

ARTEMIS will also explore the Moon’s plasma wake – a turbulent cavity carved out of the solar wind by the Moon itself, akin to the wake just behind a speedboat.

Sibeck calls it “a giant natural laboratory filled with a whole zoo of plasma waves waiting to be discovered and studied.”

Another target of the ARTEMIS mission is Earth’s magnetotail.

Like a wind sock at a breezy airport, says Sibeck, Earth’s magnetic field is elongated by the action of the solar wind, forming a tail that stretches to the orbit of the Moon and beyond. Once a month around the time of the full Moon, the ARTEMIS probes will follow the Moon through the magnetotail to make observations.

“We are particularly hoping to catch some magnetic reconnection events,” says Sibeck. “These are explosions in Earth’s magnetotail that mimic solar flares, albeit on a much smaller scale.”

ARTEMIS might even see giant “plasmoids” accelerated by the explosions hitting the Moon during magnetic storms.

These space explorations may have down-to-Earth applications, the scientists say. Plasma waves and reconnection events occur on Earth, in experimental nuclear fusion chambers. Fundamental discoveries by the ARTEMIS mission could help advance research for fusion power plants.

The ARTEMIS mission is an offspring of NASA’s five-satellite THEMIS mission to study geomagnetic storms, called substorms, for which Angelopoulos is also the principal investigator.

Themis was the blindfolded Greek goddess of order and justice, an appropriate name for the THEMIS mission, which NASA says was launched February 17, 2007, from Cape Canaveral, Florida, “to impartially resolve the trigger mechanism of substorms.”

Working together, the five probes discovered previously unknown phenomena such as colliding auroras, magnetic spacequakes, and plasma bullets shooting up and down Earths magnetic tail. These findings allowed researchers to solve several longstanding mysteries of the Northern Lights.

The mission was going splendidly, says Angelopoulos, except that occasionally, the two satellites would pass through the shadow of Earth. The solar powered spacecraft were designed to go without sunlight for as much as three hours at a time, but as the mission wore on, the they were spending as much as eight hours a day in the dark.

“The two spacecraft were running out of power and freezing to death,” says Angelopoulos. “We had to do something to save them.”

The ARTEMIS mission redirects two of the THEMIS satellites to the Moon, where they will study the space environment farther from Earth than THEMIS was ever designed to do, Angelopoulos explained.

Artemis was the goddess of the Moon in ancient Greek mythology and for the NASA mission ARTEMIS stands for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun.

“Earth is protected from solar wind by the planetary magnetic field,” says Angelopolous. “The Moon, on the other hand, is utterly exposed. It has no global magnetism.”

Studying how the solar wind electrifies, alters and erodes the Moon’s surface could reveal valuable information for future explorers and give planetary scientists a hint of what’s happening on other unmagnetized worlds around the solar system.